The crystallographic and metallurgical properties of certain cast and welded engineering materials, such as thick austenitic stainless steels make meaningful nondestructive examination by ultrasonic techniques extremely difficult because of varying attenuation introduced into the ultrasonic beam by the normal properties of the material. The attenuation varies from place to place on the part being examined in a random or unpredictable manner and has the greatest magnitude for ultrasonic examination in the shear-wave mode. The shear-wave mode is often the most useful for detecting important structural discontinuities. The difficulty arises in the fact that the effect of varying sonic attenuation in the material effectively destroys the calibration of the instrument and makes meaningful interpretation of the results difficult, if not impossible.
Standard industrial practice at this time uses hand-held transducers and manual interpretation of the instrument reading by a well-trained and highly-skilled ultrasonic technician, who often must correlate many different readings and other data to make a successful examination at each point. The process is time consuming and quite often not meaningful, particularly when examining thick sections. Geometrical constraints often complicate the interpretation. One case of particular significance arises when plates or pipes are joined by welding. The weld zone alone contains the crystallographic and metallurgical complications. The base metal on either side, through which the ultrasonic beam must pass to make the examination, have different values, usually constant, of ultrasonic attenuation.
It is therefore an object of this invention to provide an improved means and method for ultrasonic examination of materials.
Another object in this invention is to provide a method and means for ultrasonic examination of materials where the properties of the normal material result in varying attenuation of the ultrasonic signal as it passes through the material.